A pressurized-water reactor has its core contained by a pressure vessel to which the pipes of the reactor's coolant system connect. A break in the coolant system can result in a pressure release on the pressurized-water in the vessel so as to empty the vessel and deprive the core of cooling water.
A break in a cold pipe loop leg which returns the coolant to the pressure vessel, is particularly serious, because then the discharge from the pressure vessel is in a direction opposite to the normal coolant circulating direction. As a remedy, the prior art has proposed that the cold leg pipe of each reactor main coolant loop, be connected with the pressure vessel through a check valve which is normally open when the coolant flow is in the normal circulating direction, and which closes upon flow in a reverse direction. Therefore, in the event of a break in the cold pipe leg, the check valve closes and prevents loss of coolant from the pressure vessel.
However, the above arrangement does not protect against a break in the connection between the check valve and the pressure vessel or in the casing of the check valve.